Comment by AceJohnny2

Git has a wide open reference namespace for these kinds of ideas, and I'm always excited to see someone use it like this.

See, at core git is a collection of objects (referenced by their hash), along with references to tip-of-tree objects. These references are stored in the refs/ directory, and core git only uses a couple subdirs/namespaces under that: refs/heads/ (for branches) and refs/tags/ (for tags). Git also bundles the oft-forgotten git notes command that stores notes in refs/notes/. But you can add whatever other name under refs/ to tack on whatever functionality you want, which is what all these git-based bug-trackers do.

Side-note, Gerrit exploits this wide-open namespace for its behavior, where pushing to the virtual refs/for/ namespace will create a new Change destined for a given branch. It also uses these namespace for its internal NoteDB.